Loud speaker



y 31,1932 J. P. MINTOIQ 1,861,222

LOUD SPEAKER Filed June 25 1925 Fig. 1

I l F/g. 4 g

I I I & I 1 I INVENTOR g I JOHN P. wmou IA I By FREdl/f/VC'Y (la 44TTORNEY Patented May 31, 1932 UNITED STATESPATENT OFFICE JOHN P. MINTON,01 WHITE PLAINS, NEW YORK, ASSIGNOB TO RADIO CORPORATION OI AHEBICA,'AGOBIORATION' OI! DELAWARE LOUD SPEAKER Application filed Jane 25, 1925.Serial No 39,583.

The invention concerns an acoustic device particularly adapted to loudspeakers for radio recelvers or electric phonographs and.

has for its principal object to replace the usual 3 diaphragm andamplifying horn of such a device with a vibrating element of suflicientsize to set in motion a column of air large enough to maketlieuse of ahorn or-other amplifying means unnecessary. .10 A further object of theinvention is to provide an acoustic device of this character in whichthe vibrating element will respond readily even to the lowestfrequencies within its range of operation. 7

Still another object of the invention is to provide a vibratory systemin which the vibratory element'will freely vibrate substantially as apiston for the lower frequencies within its operating range and as 9.dia- 20 phragm for the higher frequencies, thereby giving more uniformresponse throughout its range.

Still another object of the invention is to provide a vibratory systemin which the vibratory element will freely vibrate at frequencies whosewave lengths are lar e compared with the size of the element itsel sothat all of its parts vibrate substantially in phase and with equalamplitude and which at higher fre- Rfi quencies will vibrate as adiaphragm.

v Still another object of the invention is to provide an acoustic devicewhose vibrating element is supported by springs or other devices havingjust enough tension to return it to andmaintain it in normal restposition when not subjected to any operating forces. It has been foundthatthe use of suitable diaphragms of large area in acoustic orelectro-acoustic devices makes it unnecessary to provide a horn or othersound amplifying means as the large column of air set in motion by sucha diaphragm furnishes sufiicient aeoustic energy to make amplificationunnecessary. The large diaphragm moreover. has an advantage over thesmall one in that there is less interference between the sound wavesfrom its two sides. A vibrating diaphragm, of course. emits sound 'wavesfrom its opposite sides which are out of phase with each other and asthese waves spread out in position when it has been displaced. In thisall directions those from one side cause interference with those fromthe other, resulting in considerable diminution and distortion of thesound. A large diaphragm will evince thischa'racteristic to a much lessextent than a small one and as a result give more intense radiation withless distortion. These efiects are further reduced according to theinven: tion by surrounding the diaphragm with a bafile, comprising asubstantially rigid barrie'r about the edge of the diaphragm so thatsound waves from one side will beprevented to a considerable extent fromreaching and inerfering with those emitted from the other 51 e.

Another feature of the invention resides in the method of supporting thevibratory element. The ordinary diaphragm or cone which is attached toits support by inflexible means or by means possessing an appreciableamount of restoring action will respond very well to the intermediateand higher frequencies within the ran e of audibility but it eitherfails to respond altogether to the lower frequencies or responds sofeebly to them that small intensity of sound only is obtainable andconsiderable distortion is introduced into the speech or music beingreproduced. The present inventi on contemplates attaching the diaphragmor cone to its support by springs or flexible means which have minimumpossible elastic restoring action, such action being just suflicient tomaintain the element inits normal rest position and restore it to this85 respect it is analogous to a so called dead heat instrument whosemoving element will move to a certain position and then stop deadwithout any appreciable overthrow. In the present case the diaphragm orcone will be returned to its normal rest position by just suilicientrestoring force to cause it to reach its rest position and there will besubstantially no overthrow. v

An element supported in this manner and hereinafter referred to as afreely supported body will have its restoring force confined almostwholly to the supporting means itself and will have two distinct modesof o ration within the range of audibility. At t elower 1m 7 that is thedisplacementsfrom rest position set up at its center will travel'to itsedge and back again 'to the center causing flexure of the element andsetting up sound waves in the usual manner. As the piston action isobviously well suited to the reproduction of low frequency sounds and asthe diaphragm action is well suited to the reproduction of high andintermediate frequency .sounds it will be clear that this device willrespond to all frequencies within its range in a manner admirablyadapted to the particular frequencies being reproduced and thatconsequently there w ill be a more uniform response over the completerange of audibility, resulting in a very faithful reproductionsubstantially free from distortion.

A more complete understanding of the invention may be had from thefollowing detailed description which should be read in connection withthe accompanying drawings in which Fig. 1 showsa specific embodimentaccording to the invention,

Figs. 2 and 3 a section and elevation respectively of a modification andFig. 4 shows aplurality of curves illustrat ing the action of the freelysupported vibrator element. 1i.

Fig. 1 is shown a'cabinet comprising a base 2, sidewalls 3 and 4 andtop 1. This cabinetmay include a radio receiver, electric phonograph orsimilar device indicated diagrammatically at A and B, itbeingunderstoodthat the output circuit of this device represented by wires 14 hasundulating currents therein corresponding to sounds which it is desiredto reproduce from the vibrating system. The side wall 4 of the cabinethas an aperture 15 formed therein which should preferably be as large aspossible. This aperture is covered by the grille 5 supported by suitablebrackets on the sidewall 4. Within the aperture 15 is supported thevibratory element or diaphragm 6 from whosevibrations result the soundscorresponding to electric currents in the wires 14. The element 6 issupported by springs 8 attached to lugs 7 on the vibratory element andto lugs 9 in the sidewall 4 thus providing a slightly resilient supportfor the vibratory element.

The vibration of the element 6 is caused in the example shown by theelectromagnetic device 12 whose coils are connected to the outfor eventhe lowest audiput conductors 14. This magnetic device as shown consistsof a permanent magnet having electromagnets associated therewith, butit-isobvious that other actuating'means, such as the balanced armatureor electrodynamic types, for example could readily be used. Thesedevices are well known in the art and therefore further description ofthem is unnecessary. To the vibratory element 6 is fastened an armature10 responsive to the magnetic field of the device 12. The armature 10 isfastened in any suitable manner to the element 6 by adjusting meansincluding a thumb screw. 11 by which its position with respect to themagnetic device 12 may be varied. thereby controlling the response ofthe vibratory element to the I magnetic device. The magnetic device issupported from the base 2 by the bracket 13, although obviously anyother convenient method of support could be adopted.

The supporting springs 8 should be made as light as ossible as theirpurpose is to support the dlaphragm with minimum ossible elasticrestoring force. They shoul therefore possess ust sutlicient resiliencyto main-- tain the element 6 in its normal rest position and restore itto this position without appreciable overthrow when it has beendisplaced. When these conditions are satisfied this vibrating elementalone will have a natural frequency below its operating range that isbelow the range of audibility, and in responding to the lower audiblefrequencies substantially as a vibrating'piston it will reproduce low'frequency sounds faithfully without appreciable distortion. Theintermediate and higher frequencies in the audible range will cause theelement 6 to operate as a vibratory diaphragm in the well known mannerand its natural characteristics will make the piston 'action'negligibleat these frequencies according to well known physical laws.

The action of a body thus sup orted will be clearer after aconsideration of the curves shown in Fig. 4 in which abscissas representfrequency and ordinate a function of the sound intensity which for lackof, a better name has been designated as diaphragm response. The audiblefrequencies in this graph extend from the point A to the point C and theresponse of the body acting as a piston has been respresented by curve Pand its response as a true diaphragm by curve D.

The diaphragm response necessary to give faithful and substantiallydistortionless rcproduction of sound has .been designated by the dottedline E E, that is any diaphragm response which deviates from this linemay be considered as undesired operation and any response which issimilar to it may be considered as desirable operation. This is ofcourse only an approximation as in practice the change over fromdesirable to undesirable operation will not occur for a definite type ofresponse but will be gradual. The closer the actual curve approximatesthe line E E the more satisfactory will be the performance. Thisapproximation, however,

is close enough to the actual operation to assist in understanding theactual conditions. Returning now to the curves it is apparent from curveD that if the vibratory element acted as an ordinary diaphragmthroughout the audible range there would be very good 7 soundreproduction in the region from B to C examination of the curve but verypoor reproduction in the region from A to B. There would then be verydesirable reproduction of the intermediate and higher frequencies butvery poor repro- From an duction of the lower freqienci'es.

representlng the action of a vibratory element as a true piston that issuch reproduction as depends on the movement of the diaphragm as a unitto cause all sound waves, it will be obvious that a-vibratory elementwith piston action would give very good reproduction in the region fromA to B but very poor reproduction in the region from B to C. In otherwords the vibratory piston would reproduce the lower frequencies verywell but the intermediate and higher frequencies very poorly.

A freely suspended body such as 9, diaphragm supported as explainedabove partakes of the nature of a piston as well as a diaphragm. At thelower frequencies the piston action will predominate and at theintermediate frequencies the diaphragm action will predominate and theresultant response curve will be somewhat of the form P.--F.D. From thisit will be seen that the freely suspended element will reproducefaithfully, without undue distortion and with desirable intensity allfrequencies with in the audible range covering entirely the region fromA to C.

The structure shown in Fig. 1 possesses further advantages in that thewalls of the cabinet,' particularly the portions of the side wall 4surrounding the aperture act as a bafiie to prevent interference betweenthe sound waves leaving the, front of the diaphragm and those emittedfrom the rear.

These two sets of waves on leaving their respective sides of thediaphragm will be 180 out of phase; that is as a wave, of condensationis emitted from the front face a wave of rarefaction will simultaneouslyleave the rear face. These waves spread out in all directions and, ifthevibrating element were not surrounded by some baflle means, it isobvious that the waves from its rear face would reach the area coveredby waves from its front face considerably out of phase with the latterand thereby cause considerable distortion and diminution of soundintensity. This may be corrected by providing a rigid barrier around theacoustic element so that q the waves from the rear. face will be cut offthat the path through which they must travel to reach this area will beso lengthened that their effects in interfering with the waves emittedfrom the front face will benegligible. In the present structure the wall4 surrounding the vibrating element acts as a rigid barrier or bafliecutting off the waves emanating from the rear of the element from thearea in front of it. Maximum sound intensity and minimum distortion istherefore obtained from the sound waves emitted by the front of thevibratory body.

A modification of thedevice is shown in Figs. 2 and 3 which is entirelyanalogous in its operation and possesses all the advantages of thatshown in Fig. 1 but which differs from the latter in that the loudspeaker is a separate unit and not incorporated-in the cabinet of anassociated radio receiver or similar device. Referring to these figuresthe reference numeral 20 designates a base on which is mounted thevibrating element 22 shown as of the double cone type and supported by aflat ring 21 to which it is attached by strips 23, which may be offlexible material such as rubber or leather or slightly resilientmaterial as metal. The strips 23 are secured to the ring 21 by suitableclamping members 24. While four of these attaching members have beenshown in the present instance it is obvious that more or less could beused as desired. In some cases a single one at the top may be suflicientwhile in other cases an annulus of soft leather or rubber completelyclosing the space between the cone element and the supporting ring maybe desirable. Whatever form of attachment is chosen however it mustpossess substantially the same properties as to its restoringcharacteristics as the springs 8 in Fig. 1. That is the system mustpossess just suflicient elastic restoring force. to maintain the conesin normal rest position and to return them-to this position when theyare displaced therefrom. As long as these conditions are satisfied it isevident that the cones will behave as a freely suspended body and actsubstantially as a piston in response to low frequencies and as anunclamped diaphragm in response to intermediate and high frequencies asexplained in connection with the device in Fig 1.

The supporting ring 21 is attached to the base 20 and held uprightthereon by means of brackets 27. v The operating mechanism 25 issupported on a bracket 26 and has an operating rod 28 fastened to thedouble cone 22 as shown. It is immaterial What particular form ofoperating mechanism is used, it being Moreover. the vibrating elementsneed not be' enclosed in a cabinet and therefore the supporting rin 21must be of sufiicient width to act as a ba e for preventing the soundwaves emitted from the rear of the cone member from interfering withthose emitted from the front. It will probably be necessary to make itwith an outside diameter of perhaps two feet for the large cones'now inuse. If desired however the operating mechanism of this device can beenclosed in a casing in which case the supporting ring 21 can bereplaced by onewall of the casing making the structure very similar tothat in Fig. 1.

While I have disclosed the invention in several particular forms it willbe obvious to those skilled in the art that it is capable of manymodifications, for example, the modification shown in Figs. 2 and 3 canbe used in connection with a radio cabinet as that in Fig. 1 and thevibratory system of Fig. 1 can be used as a unit as suggested in Fig. 2.

limited to the forms shown but can be of any other shape or style aslong as their supporting system possesses the characteristics explainedabove. I intend to be limited in the invention therefore only asindicated in the following claims.

Having described my invention, I claim:

1. In an acoustic device the combination of a vibratile body, means forvibrating said body, a supportingmem'ber, and means for suspending saidbody from said supporting member, said suspending means having theminimum amount of restoring action which will return said bod to itsposition of rest when moved there rom by the vibrating a means.

2. In an acoustic device the combination of a vibratile body, asupporting member, a plurality of springs for positioning said bory in apredetermined position with respect to said member, and means responsiveto operating forces for moving said body from said predeterminedposition against the action of said springs, said springs having theminimum amount of resiliency necessary to restore said body to saidpredetermined position when no operating forcesare acting on said body.

In a device for reproducing sound the combination of a diaphragm, asupporting member forming an opening slightly larger than. saiddiaphragm, means connected between the periphery of said diaphragm andsaid supporting member for holding said diaphragm in its inoperativeposition, and .a driving unit for moving said diaphragm from itsinoperative position in response to operating forces, said means havinga min: mum. restoring action to return said diaphragm to its inoperativeposition when no operating forces are acting upon .it.

4. In a device for reproducing sound the,

combination of a diaphragm having a circular periphery, a memberforminga circular aperture slightly larger than the periphery .of saiddiaphragm, a plurality of lugs fastened to said diaphragm near itsperiphery, a corresponding number of ln s fastened to said memberadjacent to sai aperture, springs fastened between the lugs on saiddiaphragm and the lugs on said member for supporting said diaphragm inits inoperative position, and means responsive to operating forces formoving said diaphragm from its inoperative position, said springs havinga minimum restoring action to return said diaphragm to its-inoperativeposition when no operating forces are acting upon it.

5. A sound reproducing devicecomprising a vibratile diaphragm, asupport, and means comprising a thin, flat, flexible strip forconnecting the diaphragm and the support whereby the diaphragmhasfreedom of vibration.

6. A sound reproducing device comprising a vibratile diaphragm, asupport, thin, flat, flexible elements secured to the edge of saiddiaphragm and to said support for holding the diaphragm in a freevibratile position.

7. A sound reproducing device comprising a vibratile diaphragm, asupport, said diaphragm having its edge spaced fromsaid support, thin,flexible strips in the space between said edge and said support andconnected-to said edge and said support for supporting the diaphragm forfree vibrations thereof.

8. A sound reproducing device comprising a vibratile diaphragm, asupport surrounding the same and spaced from the edge thereof, spacedflexible elements in said space, means for securing said elements to theedge of said diaphragm, and means for securing said elements to saidsupport, whereby said diaphragm has substantially free vibration. I

9. Sound reproducing apparatus comprising a cabinet having side wallsforming an enclosure with the top and bottom thereof,

an opening of material size in one of said side walls, a grille coveringsaid opening, a sound reproducer of the diaphragm type housed withinsaid cabinet with the diaphragm thereof adjacent saidopening, saiddiaphragm being sufficiently large to reproduce sound without the aid ofa horn, a

elements of substantially thin, flat material,

means for connecting said elements to said diaphragm, and means. forconnecting said elements to said structure. I

11. Asound reproducing device comprising avibratilc diaphragm having asubstantially conical surface, a structure spaced from said diaphragm,spaced flexible elements of thin, flat material extending outwardly fromsaid diaphragm to said structure, means for connectin one end of each ofsaid elements with said diaphragm, and means for connectin the other endof each of said elements with said structure.

12; Sound reproducing apparatus comprising a cabinet, radio receivingapparatus housed within said cabinet, an opening in said cabinet, a loudspeaker electrically connected with said radio receiving apparatus andhoused within said cabinet with its 15 diaphragm adjacent to said ening,said loudspeaker including a diap ragm sufficiently large to reproducesound at loudspeaker volume without the aid of a horn, supporting meansadjacent to said opening, and flexible suspending means having a lowrestoring force connected between sald sup porting means and saiddiaphragm, whereby said diaphragm is. supported substantially adjacentto said opening.

L3. Sound reproducing ap aratus comprising a cabinet having a wa 1, anopening of'material size in said wall, a loudspeaker 7 including adiaphragm and operating means therefore housed within said cabinet, said30 diaphragm being sufliciently large to reproduce sound at loudspeakervolume without the aid of a horn, radio receiving apparatus housedwithin said cabinet, electrical connections from said radio receivingapparatus to the diaphragm operating means, supporting means adjacent tothe opening in said wall, and flexible suspending means having a lowrestoring force connected substantially between the peripheral portionofsaid diaphragm and said sup orting means whereby the peri hery of saiddiaphragm is positioned a jacent to said opening but spaced therefrom.

14. Sound reproducing apparatus comprising a cabinet, radio receivingapparatus house within said cabinet, an opening in said cabinet, a loudsaker electrically connected with said ra io receiving apparatus andhoused within said cabinet with its diaphragm adjacent to said 0 ning,said loudspeaker including a diap ragm suflicientl large to reproducesound at loudspeaker vo ume without the aid of a horn, sup orting meansfor the diaphragm having a ow restoring force and operating means forthe diaphragm housed within said cabinet.

JOHN 1 MINTON.

15. Sound reproducing apparatus comprising a cabinet having a frontwall, an opening of material size in said front wall, a loudspeakerincluding a diaphragm and a driving unit housed within said cabinet,said diaphragm being sufiiciently lar to reproduce sound at loudspeakervcfi ume without the aid of a horn, sup orting means adjacent to saidopening in e front wall,

hery of sald diaphragm is posilac

